Microstructure and magnetic properties of FeCo/Ti thin film multilayers annealed in nitrogen

Multifunctional nanocomposites consisting of at least one ferromagnetic phase (e.g. FeCo) and one protective, wear resistant phase (e.g. TiN) are of interest for applications as sensors or actuators in harsh environments. This paper reports on the fabrication and characterization of nanocomposite thin films, prepared from FeCo/Ti metallic precursor multilayer composition spreads using a combinatorial sputter-deposition system. After deposition, the composition spread was annealed in nitrogen (5 × 10⁵ Pa pressure) at 850 °C for 1.5 h, leading to preferential nitriding of Ti to TiN, thus forming the protective phase. Automated energy dispersive X-ray analysis, Auger electron spectroscopy, X-ray diffraction measurements, transmission electron microscopy (TEM) and vibrating sample magnetometry were used for the characterization of the as deposited and nitrided composition spreads. As an unexpected result, the appearance of a Heusler phase (Co₂FeSi) in the nanocomposite was observed by TEM. After N₂ annealing, the nanocomposites show reduced saturation magnetization values μ₀M_S between 0.5 and 0.95 T and improved coercive field values μ₀H_c between 4 and 13.8 mT, dependent on the TiN content.